Background: Obesity has a variety of adverse health outcomes, but to the authors' knowledge, the effect of obesity on outcome in patients with advanced prostate cancer is not known. For this reason, the correlation between an elevated body mass index (BMI) and clinical outcomes in patients with metastatic, castration-recurrent prostate cancer (CRPC) was evaluated.
Methods: A total of 1226 men with CRPC who were enrolled in 9 prospective clinical trials conducted by the Cancer and Leukemia Group B (CALGB) for the treatment of metastatic disease were considered. Eligible patients had progressive prostate cancer during androgen deprivation therapy (with documented castrate levels of testosterone); an Eastern Cooperative Oncology Group performance status of 0 to 2; and adequate hematologic, renal, and hepatic function. Patients were classified based on BMI as normal (18.5-24.9 kg/m(2)), overweight (25-29.9 kg/m(2)), and mildly to severely obese (> or =30 kg/m(2)).
Results: Approximately 24% of the patients had a normal BMI, 43% were overweight, and 33% were mildly to severely obese. On multivariable analysis, BMI was found to be a statistically significant predictor of overall survival and prostate cancer-specific mortality. Compared with men with normal BMIs, the hazard ratios for death for overweight men and mildly to severely obese men were 0.80 (95% confidence interval [95% CI], 0.68-0.93; P = .001) and 0.80 (95% CI, 0.68-0.94; P = .010), respectively.
Conclusions: In patients with metastatic CRPC, obesity (as defined by an elevated BMI) appears to have a protective effect against overall mortality and prostate cancer-specific mortality. Alternatively, a higher BMI may reflect different cancer biology (ie, the lack of cachexia-producing substances). Further studies to gain a more comprehensive understanding of the mechanisms behind these clinical observations are needed.